Background and Objective The purpose of this study was to determine irradiation parameters of a 780 nm low power CW diode laser (6.5 mW) leading to enhanced proliferation of cultured normal human keratinocytes (NHK). The possible role of reactive oxygen species (ROS) in this response was evaluated. Study Design/Materials and Methods: NHK were exposed to a single dose of 0 to 3.6 J/cm2 (0–180 sec) of irradiation. Proliferation parameters studied were: incorporation of 3H‐thymidine during 6–24 hr following irradiation; percentage of dividing cells and number of cells, 24 hr and 48 hr following irradiation, respectively. Results Proliferation of NHK exposed to 0.45–0.95 J/cm2 was significantly enhanced by 1.3–1.9‐folds relative to sham‐irradiated controls, as inferred from parameters studied. Exposure to other energy densities was considerably less affective in enhancing proliferation parameters. Added enzymatic antioxidants, superoxide dismutase or catalase, scavenging superoxide anions and H2O2, suppressed this enhanced proliferation. Added scavengers (α‐tocopherol acetate, scavenging lipid peroxidation, or sodium azide, histidine, mannitol, scavenging singlet oxygen, superoxide anions, and hydroxyl radicals, respectively), or N‐acetyl cysteine, the thiol‐reducing agent, suppressed the response, but to different extents. Conclusions The results indicate that 780 nm low power diode laser irradiation enhanced keratinocytes proliferation in vitro, with an apparent involvement of ROS in this response, and comparably, might be used to promote their proliferation in vivo to enhance wound healing. Lasers Surg. Med. 22:212–218, 1998. © 1998 Wiley‐Liss, Inc.